Defined as the level that takes the most time being not fun.
A loooooooong level with nothing but doors, pipes, and a flag would fit the criteria better than kaizo-hell.
That is basically the gist of the levels he makes.
Some of them make use of P-Switchs in such an evil way that to live you are forced to constantly go back and forth through a warp pipe for about 6 IRL minutes to avoid instant death before the P-Switch wears out(due to the timer freezing every time you go through the pipe)